The present invention is directed to the electrocoating arts, and more particularly to an improved method of simultaneously electrocoating a multi-material workpiece formed from a non-conductive component, and also from a conductive component, by electrocoat bath deposition or by spraying. Such multi-material workpiece may preferably comprise an automobile chassis, or other automotive components.
In the prior art, and especially in the automobile manufacturing art, certain problems have appeared in production of automobile chassis and components. Specifically, for reasons of cost and to impart desirable properties to various automobile components, polymeric or plastic components have been used and are now being used for parts which in the past have been formed from metal. The result is that the automobile chassis may have, for example, polymeric front and rear bumper components, polymeric interior trim, polymeric steering column components, and other automobile components formed from polymeric or plastics materials. Indeed, such components may be formed from different types of polymers to impart different physical characteristics to different parts.
Automobile manufacturers have deemed it beneficial to attempt to provide the same general appearance to the polymeric components as that of the metallic components. One difficulty in providing such uniform appearance is that the metallic components may be readily electrocoated, as they are conductive, but the polymeric components in the past could not be electrocoated, as they were not electroconductive. The result was that the polymeric components had to be coated separately, by other techniques, and by different coating compositions, and at different times, from the metallic components. The result in many instances was less than satisfactory in the prior art as the polymeric components did not "mesh" in physical appearance with the metallic components. A further problem was that additional equipment and facilities had to be provided for at least one separate coating operations--one operation for electroconductive materials and at least one other for the non-electroconductive materials.
One object of the improved methods and compositions of the present invention is to materially alleviate the difficulties associated with prior art techniques, and more particularly to lower the costs associated therewith, increase the efficiency of the respective operations, to provide an improved final product, and to provide primer coating compositions having a wide applicability as conductive coatings and/or substrates.